OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.10 Component testing – Page 161
2.3.5 Higher static strength values after long term exposure may be used if experimental evidence can be
provided. A procedure to obtain strength data after long term exposure is suggested in Sec.4 [3.4] and [3.9].
3 Verification of analysis by testing and updating
3.1 Verification of design assumptions
3.1.1 Tests under this category are carried out to verify that the assumptions on which the design is based are
correct and that no important aspects of the design have been overlooked. Verification tests should be carried
out to compensate for:
— incorrect description of, or an unsatisfactory large uncertainty in the failure mechanisms
— incorrect description of load combinations or corresponding large uncertainties
— incomplete understanding of the effect of the environment
— lack of experience of similar structures or components
— uncertainty in the accuracy of modelling large stress gradients
— assumptions that can be questioned or are difficult to document
— unknown effect of large scale manufacturing procedures.
3.1.2 Tests under this category are carried out to verify that the analysis tools predict the response to the most
critical load cases and environments in a correct or conservative manner. This type of testing shall be done if
the particular analysis method has never been used for a similar structure and load situation before.
3.1.3 As it is not possible to test all load conditions that the structure will experience, the most critical load
conditions should be selected. The selection shall be based not only on the most critical loads the structure is
most likely to see. It shall also show that critical failure modes that can be caused by secondary loads are
adequately modelled ([1.2]).
3.1.4 It may be necessary to test more than one aspect of an analysis. This may mean that two or more separate
test programmes should be carried out, unless both aspects can be evaluated in one test. The remaining parts of
this section explain the requirement for one test programme.
Guidance note:
The end fitting of a pipe has been analysed. There is uncertainty about fatigue performance and long term static
strength. In this case both aspects should be tested separately.
There is uncertainty about long term fatigue performance of new specimens and of specimens with impact damage.
In this case the specimen can most likely be exposed to impact before the fatigue testing and only one test programme
is needed. This test programme would cover both aspects in a conservative way.
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3.1.5 In general the environment defined in Sec.3 [10] should be represented in a realistic manner. The
environmental effect can be accounted for either by:
— carrying out tests on components that have been subjected to a representative ageing (accelerated or not
accelerated)
— carrying out tests on components combined with ageing (accelerated or not accelerated). An example is the
standard techniques used for qualification of pipes.
Since these tests are used to increase the confidence in calculation techniques other environments may be
chosen if it can be demonstrated that the effects of the real environment can be predicted in a conservative way
by a combination of analytical tools and the test results obtained from a special test environment.
3.1.6 The following steps shall be followed when defining and carrying out test under this category:
1) The load condition(s) and environments are defined as specified in Sec.3.
2) The failure mode, failure mechanism and location of failure etc. on which the design is based are specified.
3) The number of test specimens required per load condition is specified. The number of test specimens may
have to be determined based on an engineering judgement.
4) Carry out testing.
5) Verify failure mode, failure mechanism and location of failure. If these are as predicted in 2. the
assumptions for the design are considered corroborated. If one or more of these are not as predicted in 2.
the reason for the discrepancy shall be investigated and the validity of design assumptions re-evaluated.
3.1.7 Instead of testing the full component it may be more relevant to test parts or details. Which test is the
best should to be evaluated considering relevant failure modes and all possible interaction effects.
3.1.8 The failure mode(s), failure mechanism(s) and location(s) of failure shall be recorded and verified
during/after the tests.
DET NORSKE VERITAS AS